Process flow for graphene nanoribbon fabrication. Optical microscope image (top row), cartoon top view (middle row), and cartoon side view (bottom row), for each of four major processing steps. (a) Graphene deposition on Si/SiO2 substrate. (b) E-beam lithography fabrication of metal electrodes. (c) Patterning of negative e-beam resist etch mask. (d) Removal of unprotected graphene by oxygen plasma etching. Scale bar in optical image is 20 μm, all four optical images have the same scale.